Mitotic control of human papillomavirus genome-containing cells is regulated by the function of the PDZ-binding motif of the E6 oncoprotein

Abstract

The function of a conserved PDS95/DLG1/ZO1 (PDZ) binding motif (E6 PBM) at the C-termini of E6 oncoproteins of high-risk human papillomavirus (HPV) types contributes to the development of HPV-associated malignancies. Here, using a primary human keratinocyte-based model of the high-risk HPV18 life cycle, we identify a novel link between the E6 PBM and mitotic stability. In cultures containing a mutant genome in which the E6 PBM was deleted there was an increase in the frequency of abnormal mitoses, including multinucleation, compared to cells harboring the wild type HPV18 genome. The loss of the E6 PBM was associated with a significant increase in the frequency of mitotic spindle defects associated with anaphase and telophase. Furthermore, cells carrying this mutant genome had increased chromosome segregation defects and they also exhibited greater levels of genomic instability, as shown by an elevated level of centromere-positive micronuclei. In wild type HPV18 genome-containing organotypic cultures, the majority of mitotic cells reside in the suprabasal layers, in keeping with the hyperplastic morphology of the structures. However, in mutant genome-containing structures a greater proportion of mitotic cells were retained in the basal layer, which were often of undefined polarity, thus correlating with their reduced thickness. We conclude that the ability of E6 to target cellular PDZ proteins plays a critical role in maintaining mitotic stability of HPV infected cells, ensuring stable episome persistence and vegetative amplification.

Oral fibropapillomatosis and epidermal hyperplasia of the lip in newborn lambs associated with bovine Deltapapillomavirus

“…Therefore, BPVs may interfere with ACD homeostasis generating a pool of stem cells that may be predisposed to cell transformation. Such connections between ACD and PV tumorigenesis have begun to emerge from in vitro and in vivo models 53 – 56 although future studies are needed to gain insights into the relationship, if any, between PV-associated tumorigenesis and ACD perturbation.…”

Mechanisms by which HPV Induces a Replication Competent Environment in Differentiating Keratinocytes

“…A role for the E6 PBM in productive replication has also been observed for the high-risk types HPV31 and HPV16 [ 88 , 89 ]. More recent studies demonstrated that the E6 PBM protects the mitotic integrity of keratinocytes containing HPV18 episomes, with loss of the PBM domain leading to mitotic abnormalities that prevents the expansion of suprabasal cells to support vegetative viral replication [ 90 ]. What specific PDZ proteins are targeted by E6 to preserve mitotic integrity and to promote viral replication have yet to be defined.…”

Upsetting the Balance: When Viruses Manipulate Cell Polarity Control

“…The life cycle of HPVs is completely dependent on the differentiation program of the infected epithelium, and studies of infection in organotypic raft cultures show that viruses defective in binding the polarity proteins produce fewer progeny virus and their genomes are more unstable and prone to integration in the host DNA [56][57][58].…”